As a conventional technique, a doppler ultrasonic flowmeter using the ultrasonic pulsed doppler method has been known as disclosed in Japanese Unexamined Patent Application Publication No. 2000-97742.
The doppler ultrasonic flowmeter has a configuration wherein ultrasonic pulses are cast from a transducer onto a measurement line within a flow tube, ultrasonic echo signals, i.e., the reflected-wave signals from suspended fine particles in a fluid flowing in the fluid tube are analyzed so as to calculate the flow-speed distribution and the flow of the fluid flowing along the measurement line based upon the positions and velocities of the suspended fine particles. The measurement line is formed by an ultrasonic-pulse beam cast from the transducer.
The doppler ultrasonic flowmeter may be applied to an opaque fluid and an opaque-fluid tube, as well as having the advantage of measuring the flow of a fluid flowing a fluid tube in a non-contact manner. Furthermore, the doppler ultrasonic flowmeter has the advantage of measurement of the flow-speed distribution of an opaque fluid and the flow thereof, e.g., measurement of the flow of liquid metal such as mercury, sodium, and so forth, as well as having functions for measuring the flow-speed distribution and the flow of a fluid flowing in the flow tube with measurement along the measurement line.
The doppler ultrasonic flowmeter has the advantage of detecting change in the flow-speed distribution over time along the measurement line formed by the ultrasonic pulses cast onto the fluid from the transducer, and accordingly, it is hoped that the doppler ultrasonic flowmeter can be applied to measurement of a transient flow of a fluid flowing through the flow tube, and measurement of the flow-speed distribution and measurement of the flow in a turbulent situation.
An arrangement example of the ultrasonic flow-speed distribution meter and the ultrasonic flowmeter described above is disclosed in Japanese Unexamined Patent Application Publication No. 2000-97742.
Measurement with the conventional doppler ultrasonic flowmeters is made under the assumption of existence of reflected ultrasonic echoes due to reflection from bubbles or particles contained in a fluid which is to be measured. Accordingly, in some cases, extremely unstable flow of the fluid which is to be measured leads to irregularities in the measurement results of the flow-speed distribution due to irregularities in density of bubbles or the like. Furthermore, with the conventional doppler ultrasonic flowmeters, measurement of the flow is made based upon the measurement results of the flow-speed distribution. Accordingly, such irregularities in the flow-speed distribution affect computation of the flow, resulting in irregularities in the measurement results of the flow, as well.
Furthermore, the conventional doppler ultrasonic flowmeter has a function for receiving ultrasonic echoes at 128 positions at best, giving consideration to a tradeoff between responsibility of measurement of the flow which changes in a short period of time and the performance of the hardware of the conventional doppler ultrasonic flowmeter. In this case, the minimum interval (which will be referred to as “channel distance” hereafter) between the measurement points for measuring the ultrasonic echoes matches the value obtained by dividing the ultrasonic speed Cw in the fluid to be measured, by twice the basic frequency f0 of the ultrasonic pulse.
Accordingly, with the conventional doppler ultrasonic flowmeter employing such a channel distance, the maximum distance of the measurement line matches 128 times the minimum channel distance, leading to a problem that measurement of the flow-speed distribution cannot be made over the entire tube in a case wherein the fluid tube is formed with a greater diameter than the aforementioned measurement line.
On the other hand, the ultrasonic speed Cw in the fluid which is to be measured, the basic frequency f0 of the ultrasonic pulses, and the incident angle α of the ultrasonic pulse, are adjusted based upon the kind of the fluid which is to be measured, the thickness and material of the tube, so as to make optimum measurement. Accordingly, conventional doppler ultrasonic flowmeters require preliminary measurement for determining the optimum settings suitable for the object which is to be measured, which is troublesome. This leads to low evaluation of ease of use, although the conventional doppler ultrasonic flowmeter has the advantage of making measurement while suppressing error without “flow correction coefficients”.
On the other hand, an arrangement may be made wherein the kind of the hardware is varied corresponding to the object to be measured and the measurement range, e.g., the doppler ultrasonic flowmeter may include multiple kinds of hardware so as to handle various tube size and various range of the maximum flow speed. However, such a configuration is undesirable from the perspective of design, costs, and the like.
On the other hand, an arrangement may be made wherein measurement is made at a greater number of measurement positions than with the aforementioned one so as to make measurement over a greater length than with the conventional one. However, such configuration is restricted by the performance of the hardware, costs, and so forth, from the perspective of responsibility of the measurement of the flow which changes in a short period of time. Even if the problems of the hardware performance and costs are solved in the future, such configuration is undesirable since such configuration is overspeced for the measurement range in which measurement can be made with the conventional doppler ultrasonic flowmeters.
On the other hand, the conventional doppler ultrasonic flowmeters have a configuration wherein measurement can be made even if a part of the fluid flows backward, i.e., a part of the fluid flows at a negative velocity. However, in actual measurement, in a case wherein the fluid flows at a sufficient flow speed, hardly any fluid flows backward. Accordingly, an arrangement may be made wherein only the forward flow is measured on the assumption that there is no backward flow in order to extend the measurement range of the flow speed. However, such configuration has a problem that determination cannot be made whether or not a backward flow occurs.
Accordingly, it is an object of the present invention to provide a doppler ultrasonic flowmeter for making more correct measurement of the flow-speed distribution or measurement of the flow regardless of irregularities in the measurement results of the flow-speed distribution, a flow-measurement method using the doppler ultrasonic flowmeter, and a flow-measurement program employed for the doppler ultrasonic flowmeter.
Furthermore, it is another object of the present invention to provide a doppler ultrasonic flowmeter having a function for automatically calculating setting values corresponding to the properties of the object to be measured, a flow-measurement method using the doppler ultrasonic flowmeter, and a flow-measurement program employed for the doppler ultrasonic flowmeter.
Furthermore, it is another object of the present invention to provide a doppler ultrasonic flowmeter having a greater measurement range than with the conventional one without extending the performance of the hardware thereof, a flow-measurement method using the doppler ultrasonic flowmeter, and a flow-measurement program employed for the doppler ultrasonic flowmeter.
Furthermore, it is another object of the present invention to provide a doppler ultrasonic flowmeter having functions for extending the measurement range for the flow speed in a case wherein there is no flow at a negative velocity while detecting whether or not there is any flow at a negative velocity, a flow-measurement method using the doppler ultrasonic flowmeter, and a flow-measurement program employed for the doppler ultrasonic flowmeter.